Method and apparatus for removing photoresist

ABSTRACT

A method and apparatus remove photoresist from a wafer. A process gas containing sulfur (S), oxygen (O), and hydrogen (H) is provided, and a plasma is generated from the process gas in a first chamber. A radical-rich ion-poor reaction medium is flown from the first chamber to a second chamber where the wafer is placed. The patterned photoresist layer on the wafer is removed using the reaction medium, and then the reaction medium flowing into the second chamber is stopped. Water vapor may be introduced in a salvation zone provided in a passage of the reaction medium flowing down from the plasma such that the water vapor solvates the reaction medium to form solvated clusters of species before the reaction medium reaches the wafer. The photoresist is removed using the solvated reaction medium.

BACKGROUND OF THE INVENTION

The present invention relates to the formation of semiconductor devices.More specifically, the present invention relates to removal ofphotoresist.

During semiconductor wafer processing, features of the semiconductordevice are defined in the wafer using well-known patterning and etchingprocesses. Photoresist (PR) is used to protect some areas of the waferfrom etch chemistries so as to define the features. Photoresist is alsoused as ion implantation masks for implanting a dopant into a siliconsubstrate. Conventionally, photoresist masks are removed by a “wet”process in back end of line (BEOL) processing, for example, aftermetallization, while a “dry” process is used in front end of line (FEOL)processing, for example, after ion implantation that characterizesdevices. However, dry stripping may be used in the BEOL processing, andwet stripping may be used in the FEOL processing. Dry photoresist stripmay be conducted either in a downstream environment or in a direct lowbias-potential plasma. In FEOL processing, active areas (Si or SiGe),doped or undoped, are subjected to various levels of implants, followedby photoresist strip and post strip cleans.

Effects on active area from dry or wet processes can be detrimental froma material or dopant loss prospective. Material loss can occur as theactive area is subjected to repetitive strip-and-cleans or etchprocesses. Material loss is generally defined as the conversion ofactive species such as silicon or dopants to their inactive compoundssuch as oxides. As material loss increases, various devicecharacteristics, such as drive current, leakage, resistivity, and shortchannel effects, also change. Device sensitivity to material lossincreases even further as device geometries decrease 45 nm and beyond,where junctions are shallower and more lightly doped by high-flux,low-energy ion implantation. Active area characteristics are aprecision-engineered part of any device for optimum performance, andtherefore, material loss due to FEOL processing—such as post ion implantstrip (PIIS), may be detrimental to device performance. Furthermore, theions implanted in the photoresist chemically modify the near-surfaceregions, causing decomposition, cross-linking, etc., of the photoresist.Such chemically modified regions form a hard crust, where the polymermay become graphitic in nature. Such a hard crust is typically formed inthe upper resist region and at exposed sidewalls.

In order to avoid material loss due to ion bombardment in dry stripprocesses, improved wet processes with a hot sulfuric acid have alsobeen used. However, typical wet photoresist strip chemistries, such ashot Piranha solutions (H₂SO₄:H₂O₂), do not work well when such crustsexist. In order to strip such crusts, aggressive plasma stripchemistries are being used, which typically include highly oxidizingradicals. To enhance the crust strip, the wafer may be heated, andfluorine (F)-containing species may be added to the plasma. However, useof such harsh chemicals (i.e., reduction or fluorination) and/oroxidation leads to Si material loss as well as dopants and Ge, whichimpacts device performance.

SUMMARY OF THE INVENTION

To achieve the foregoing and in accordance with the purpose of thepresent invention, a method for removing photoresist from a wafer isprovided. The wafer has a patterned photoresist layer thereon. A processgas containing sulfur (S), oxygen (O), and hydrogen (H) is provided, anda plasma is generated from the process gas in a first chamber. Aradical-rich ion-poor reaction medium is flown from the first chamber toa second chamber where the wafer is placed. The patterned photoresistlayer on the wafer is removed using the reaction medium, and then thereaction medium flowing into the second chamber is stopped.

In another manifestation of the invention, water vapor is introduced ina salvation zone provided in a passage of the reaction medium flowingdown from the plasma such that the water vapor solvates the reactionmedium to form solvated clusters of species before the reaction mediumreaches the wafer. The photoresist is removed using the solvatedreaction medium. The salvation zone may be provided in the first chamberdownstream of the plasma, and the reaction medium is solvated before thereaction medium enters into the second chamber. Alternatively, thesalvation zone may be provided in the second chamber.

In another manifestation of the invention, an apparatus for removingphotoresist from a wafer is provided. The apparatus includes a firstchamber for generating a plasma from a process gas, a gas source, asecond chamber, and a reaction medium distribution section. The firstchamber has a gas inlet, and the gas source is in fluid connection withthe gas inlet. The gas source provides the process gas containing sulfur(S), oxygen (O), and hydrogen (H) into the first chamber. The waferhaving a patterned photoresist layer thereon is placed in the secondchamber. The reaction medium distributing section flows a radical-richion-poor reaction medium from the plasma in the first chamber to thesecond chamber. A water vapor inlet is provided to the second chamber orthe reaction medium distribution section. The water vapor inletintroduces water vapor in a salvation zone provided in a passage of thereaction medium flowing from the plasma to the wafer such that the watervapor solvates the reaction medium to form solvated clusters of speciesbefore the reaction medium reaches the wafer. The water vapor inlet mayinclude a nozzle which is configured to inject the water vapor so as tocondensate as clusters around the species.

These and other features of the present invention will be described inmore detail below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIGS. 1A and 1B are schematic cross-sectional views of examples of asubstrate having a photoresist mask for ion implantation.

FIG. 2 is a high level flow chart of a process that may be used in anembodiment of the invention.

FIG. 3 is a schematic cross-sectional view of a plasma processing modulewhich may be used for performing the photoresist removal in accordancewith one embodiment of the present invention.

FIGS. 4A and 4B schematically illustrate examples of a downstream,inductively coupled plasma processing module which may be used forperforming photoresist removal in accordance with another embodiment ofthe present invention.

FIG. 5 schematically illustrates another example of a downstream,inductively coupled plasma processing module which may be used forperforming photoresist removal in accordance with yet another embodimentof the present invention.

FIG. 6 schematically illustrates a downstream photoresist strippingchamber (“downstream chamber”) which may be used for performingphotoresist removal in accordance with yet another embodiment of thepresent invention.

FIGS. 7A-7C schematically illustrate other examples of a plasma module(stripper module) having temperature control which may be used forperforming photoresist removal in accordance with one embodiment of thepresent invention.

FIG. 8 is a flow chart of the salvation process of the reaction mediumbeing transported from the plasma to the wafer in accordance with oneembodiment of the present invention.

FIG. 9 schematically illustrates an example of the plasma processingmodule having an additional water vapor inlet in accordance with oneembodiment of the present invention.

FIG. 10 schematically illustrates another example of the plasmaprocessing module in which the injection port is used as an additionalwater vapor inlet in accordance with one embodiment of the presentinvention.

FIGS. 11A-12 schematically illustrates other examples of plasmaprocessing modules having a water vapor inlet in accordance withembodiments of the present invention.

FIG. 13 schematically illustrates an example in which the second chamberof the plasma module includes more than one baffles (gas distributioncomponents).

FIGS. 14A-14B schematically illustrate other examples of a plasmaprocessing module in which an additional gas injection port is used as awater vapor inlet, in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

FIGS. 1A and 1B schematically illustrate a cross-sectional view ofexamples of a substrate 10 having a photoresist mask 12 for ionimplantation. The substrate 10 may also include a thin dielectric layer14. The photoresist mask 12 has features which define active areas 16where dopants are injected, as shown in FIG. 1A. The photoresist mask 12may also be used, as shown in FIG. 1B, for example, to protect a p-typedevice area 18 when active areas 20 for an n-type device are formed byion implantation. After the ion implantation, the near-surface regionsof the photoresist mask are chemically modified by ion injection,forming a hard crust 22 covering a bulk portion 24.

In general, downstream photoresist stripping is performed by dischargingoxygen with fluorocarbon addition in a microwave or RF discharge zone.The radicals from the plasma are transported to a process chamber, whereions are typically left behind. In order to facilitate an acceptablereaction rate, the wafer may be heated up to 300° C. Material lossduring downstream strip occurs by diffusion of radicals (O*) intosilicon, which convert the silicon into silicon dioxide, where the hightemperature increases the diffusion. Alternatively, if the direct lowbias-potential plasma strip is used, material loss occurs due to chargedchemical species (O⁺ or O₂ ⁺) from the plasma penetrating through thethin dielectric layer into the active area.

In both types of dry strip the radials or ions react with the Si, Ge, ordopants, and basically incapacitate them. An example for such chemicalspecies can be oxidizing radicals that are driven through the thindielectric layer by sufficient thermal energy to react with or consumeactive area constituents. The active area constituents are oxidized oreven removed during dry strip. Results of such an action lead to theloss of active area Si or Ge. Reducing species (i.e., hydrogen) can beequally as disruptive to cause material loss in the active areas,although this is not through oxidation. In addition, as an alternativeto dry photoresist removal, wet processes have been developed usingaqueous solutions of sulfuric acid and peroxide, for example, chemistryknown as SHARK, purportedly causing minimum silicon loss. However, thetechnology is under development and does not work well when photoresistis hardened or a hard crust is formed when implanted at higher doses, asdescribed above.

Thus, in FEOL post ion implant strip processing, Applicants have studiedand developed processes for removing a hardened photoresist (PR) layerand the remaining bulk photoresist, without adversely affecting (orremoving) any exposed dielectric layer over the underlying active areaSilicon, which may or may not include N or P dopants and/or Ge. Inaddition to stringent material loss goals, it is required that the stripprocess not result in making a residue layer hard.

Embodiments of the present invention utilize a downstream plasma modulehaving a plasma discharge section upstream of a reaction chamber.Embodiments of the invention use a novel process gas containing sulfur(S), oxygen (O), and hydrogen (H).

To facilitate understanding, FIG. 2 is a high level flow chart of aprocess that may be used to remove photoresist from a substrate inaccordance with an embodiment of the present invention. The wafer has apatterned photoresist thereon. The photoresist may be used as an ionimplantation mask prior to the photoresist removal, and may have a bulkportion and a crust portion covering the bulk portion, for example, asshown in FIG. 1A or 1B. However, it should be noted that the presentinvention is also applicable to other photoresist removal, for example,photoresist strip in the BEOL processes. Referring back to FIG. 2, aprocess gas containing sulfur (S), oxygen (O), and hydrogen (H) isprovided (step 202). For example, the process gas may contain SO₂, H₂Oand O₂. The process gas may further contain fluorine containing gas, forexample, NF₆, NF₃, or fluorocarbon, for example, CF₄. More generally,fluorocarbon may be expressed as C_(x)F_(y)(x≧1, y≧1) and/orC_(x)F_(y)H_(z)(x≧1, y≧1, z≧1). The source gas may further contain othercomponent gases such as H₂ and NH₃.

A plasma is generated from the process gas in a first chamber (step204). The plasma may be discharged using a microwave, an inductivedischarge (RF energy), DC discharge, or some other high densitydissociative remote source. A radical-rich ion-poor reaction medium isflown from the first chamber to a second chamber where the wafer isplaced (step 206). The wafer has a patterned photoresist layer thereon.The patterned photoresist layer is removed using the reaction medium(step 208). Then, the flow of the reaction medium into the secondchamber is stopped (step 210). Additional cleaning process(es) may beperformed after the photoresist removal using the reaction medium (step212).

FIG. 3 is a schematic cross-sectional view of a plasma processing module100 including a plasma chamber 102 which may be used for performing thephotoresist removal in accordance with one embodiment of the presentinvention. The plasma chamber 102 includes chamber walls 104 and adielectric window 106. The plasma processing module 100 includes a feedgas inlet 108 for allowing feed gases to flow into the chamber 102. Anexhaust port 110 exhausts gases from the chamber 102. An inductivesource 112, typically taking the form of a coil positioned on thedielectric window 106, is used to energize the feed gases within thechamber 102 and ignite a plasma within the chamber 102. In this example,the inductive source 112 is powered by an RF power supply 114.

The inductive source 112 causes the plasma within the chamber 102 toform a plasma having a primary dissociation zone 116. This primarydissociation 116 zone is the region within the chamber 102 that theplasma most efficiently dissociates the feed gases. In the case wherethe inductive source 112 takes the form of a coil attached to thedielectric window 106, the primary dissociation zone 116 takes the formof a generally donut shaped region located within the chamber 102directly below the coils of the inductive source 112.

The plasma processing module 100 may also include a liner 118, such as aquartz liner, or any other available material, for protecting the wallsof the plasma chamber from the plasma and reducing the recombination ofneutral radicals like O or OH. A chuck 120 is positioned in the bottomof the chamber 102 and is configured to support a semiconductorsubstrate 122. As is known in the art, the chuck 120 may be heated toimprove the efficiency of the process. The plasma processing module 100also includes a quartz baffle 124 located above the substrate 122. Thebaffle 124 includes a plurality of openings formed through the baffle124 which cause any gases flowing through the chamber 102 to beredistributed so that the gases flow more evenly over the substrate 122than would be the case if the baffle 124 were not included in the plasmaprocessing module 100. The baffle 124 partially shields the substrate122 from direct exposure to the plasma. Thus, in this example, theplasma chamber 102 above the baffle 124 is considered as a firstchamber, and a region below the baffle 124 where the substrate 122 isplace on the chuck 120 is considered as a second chamber.

In accordance with one embodiment of the present invention, a novel gascombination containing sulfur (S), oxygen (O), and hydrogen (H), forexample, a process gas containing feed gases: SO₂, H₂O and O₂ isintroduced via the feed gas inlet 108. One of the objectives of usingH₂O is to passivate active area silicon by “sealing” dangling Si bonds.The other objective is to generate relatively large (in contrast to theoxygen radical) powerful reagents which can attack the carbon withinphotoresist, but cannot readily diffuse into active area silicon. Anoptional fluorine containing gas may also be introduced into thedischarge (dissociation zone 116) in the plasma chamber 102 via the feedgas inlet 108.

The process gas is dissociated in the primary dissociation zone 116 soas to form a radical-rich ion-poor reaction medium. In thisspecification and claims, “radical-rich ion-poor” means that the radicalconcentration (radicals/cm³) is greater than the ion density (ions/cm³)at least by the factor of E2 (10²), preferably by the factor E5 (10⁵) orgreater, more preferably by the factor of E5 (10⁵) to E8 (10⁸),depending on the pressure, dissociation efficiency, and recombinationrate. For example, the ion densities provided for the radical-richion-poor medium may be less than 10E7 (10×10⁷) ions/cm³, preferably lessthan 10E6 (10×10⁶) ions/cm³, while the range of radical concentrationsmay be 5E13 (5×10¹³) to 5E15 (5×10¹⁵) radicals/cm³, preferably 1E14(1×10¹⁴) to 1E15 (1×10¹⁵) radicals/cm³. However, when the bias isapplied, as described below, the ion density may be in the range ofabout 10E9 (10×10⁹) to 10E10 (10×10¹⁰) ions/cm³. The radical-richion-poor reaction medium also includes a reaction medium in whichsubstantially no ions are present. There are many reactions with thedischarge products which will form a variety of strongly reactivespecies. Some of these compounds are strong reducing agents, some arevery strong hydrogen donors, while others are oxidizing agents. Bycontrolling the reactive mix it is possible to balance oxidation andreduction at the active area while effectively decomposing thephotoresist. A plasma with SO₂, H₂O and O₂ as feed gases will generateradicals: HSO₄. monosulfate radical with properties of sulfuric acid,HSO₃. bisulfite radical, HO. hydroxyl radical; and O. oxygen radical.The HSO₄. and HSO₃. radicals are strong hydrogen donors such that it canhydrogenate the carbon in the photoresist. Additionally the HSO₄.radical is a strong oxidizing compound such that it along with HO. andO. oxidize the weakened carbon. It should be noted that SO₂, not otheroxides of sulfur, needs to be present with H₂O in order to facilitatethe appropriate reaction.

HSO₄.+C—C→H—C—C+SO₄.→CO₂+OH+SO

HSO₃.+O—Si—Si→H—Si—Si+SO₄.

The radical-rich ion-poor reaction medium is flown from the primarydissociation zone 116 of the plasma chamber 102 through the baffle 124to the reaction zone 126 where the substrate 122 is placed, as shown inFIG. 3. Since the baffle 124 partially shields ions from reaching thesubstrate, the reaction zone 126 can be considered as a second chamberin this example. The patterned photoresist layer on the substrate 122 isremoved using the reaction medium.

FIG. 4A schematically illustrates a downstream, inductively coupledplasma processing module 140 which may be used for performingphotoresist removal, in accordance with another embodiment of thepresent invention. For illustrative purposes, like reference numeralswill be used throughout the various figures for like components suchthat those of ordinary skill in the art understand the similarcomponents and functions thereof without additional explanation.

Generally, the plasma processing module 140 is similar to the plasmaprocessing module 100 described above, except that the plasma chamber102 is divided into a first (upper) chamber 142 for plasma generationand dissociation, and a second (lower) chamber 144 for processing(photoresist removal), by a plasma containment plate 146, as shown inFIG. 4A.

Similarly to the plasma processing module 100, the plasma processingmodule 140 includes feed gas inlet 108 for allowing feed gases to flowinto the first chamber 142. Exhaust ports 110 exhausts gases from thesecond chamber 144. Inductive source 112, in this case taking the formof a coil positioned above the dielectric window 106, is used toenergize feed gases within the first chamber 142 and generate a plasmawithin the first chamber 142 from the feed gases. In this example, theinductive source 112 is powered by RF power supply 114 which takes theform of a transformer coupled source. Typical inductive source powerranges from about 250 W to about 5000 W or more. Similarly to theprevious embodiment, the specific configuration and shape of inductivesource 112 causes a plasma having primary dissociation zone 116 in thefirst chamber 142. During plasma processing, the gas pressure within thefirst chamber 142 and the second chamber 144 may be from about 10 mT toabout 10 T or more, but typically the operating pressure is about 1 T.The feed gas flow may range from about 100 standard cubic centimetersper minute (sccm) to about 10,000 sccm or more for a 300 mm substrate(wafer).

An internal port 148 that interconnects the first chamber 142 and thesecond chamber 144 is provided substantially at the center of the plasmacontaining plate 146. The internal port 148 allows the reaction mediumgenerated in the first chamber 142 to flow into the second chamber 144during the processing of the substrate 122. The second chamber 144 mayhave a baffle 124. The reaction zone (not shown in FIG. 4) below thebaffle 124 may be considered as part of the second chamber, oralternatively, a third chamber.

As shown in FIG. 4A, the feed gas inlet 108 may be located such that theflow of any feed gases fed into the first chamber 142 is directedsubstantially through the primary dissociation zone 116 toward theinternal port 148 as indicated by the arrows. The plasma generated inthe first chamber 142 produces a reaction medium from the feed gases,and the reaction medium is transported from the first chamber to thesecond chamber via the internal port 148. In this embodiment, the feedgases may be SO₂, H₂O and O₂ which are introduced via the gas feed inlet108. The optional fluorine containing gas may also be provided throughthe gas feed inlet 108.

Additionally, the chamber walls 104 and the plasma confinement plate 146may be grounded. This grounding of the walls attracts any chargedspecies causing them to collide with the walls thereby helping toprevent the charged species (ions) from flowing from the first chamber142 into the second chamber 144.

The reaction medium introduced into the second chamber 144 is thusfurther radical-rich ion-poor, and preferably in accordance with anembodiment of the present invention, the reaction medium containssubstantially no ions or charged particles.

As shown in FIG. 4A, the second chamber 144 has a quartz baffle 124located above the substrate 122. The baffle 124 includes openings formedthrough baffle 124 which cause the reaction medium flowing through thesecond chamber 144 to be redistributed more evenly over the substrate122 than would be the case without the baffle 124.

In accordance with another embodiment of the present invention, somefeed gases are injected into the plasma discharge (dissociation zone116), while other gases may be injected downstream of the discharge.FIG. 4B schematically illustrates another example of plasma processingmodule 160 similar to the plasma processing module 140, in whichconfiguration of the feed gas inlet 108 and the internal port 148 isdifferent, and an additional injection port 150 is provided to thesecond chamber 144. In this example, the feed gas inlet 108 is providedat substantially the center of the top of the first chamber 142, and theinternal port 148 is provided at the both sides (or periphery) of theplasma containment plate 146. The additional injection port 150 isprovided on the top wall of the second chamber 144. In this example, allof the feed gases may be provided through the feed gas inlet 108.Alternatively, the fluorine containing gas may be introduced downstreamof the plasma into the second chamber 144 via the additional injectionport 150. Other features are similar to those of the plasma processingmodule 140 described above.

FIG. 5 schematically illustrates another example of a downstream,inductively coupled plasma processing module 180 which may be used forperforming photoresist removal, in accordance with another embodiment ofthe present invention. For illustrative purposes, like referencenumerals will be used throughout the various figures for like componentssuch that those of ordinary skill in the art understand the similarcomponents and functions thereof without additional explanation.

Generally, the plasma processing module 180 is similar to the plasmaprocessing modules 140 and 160 described above, except that the internalport 148 extends downward from an upper part of the first chamber 142 tothe second chamber 144 so as to have an opening on the top wall of thesecond chamber 144.

As shown in FIG. 5, the feed gas inlet 108 and the internal port 148 areprovided to the first chamber 142 such that the flow of any feed gasesfed into the first chamber 142 passes substantially through the primarydissociation zone 116 to the internal port 148. For example, the openingof the gas feed inlet 108 and the exit to the internal port 148 may belocated on the opposite side of the first chamber 142 across the primarydissociation zone 116. Furthermore, as shown in FIG. 5, the plasmaprocessing module 180 further includes an injection port 150 connectedto the passageway of the internal port 148 between an exit from thefirst chamber 142 and an opening to the second chamber 144.

The plasma generated in the first chamber 142 produces a reaction mediumfrom the feed gases, and the reaction medium is transported from thefirst chamber 142 to the second chamber 144 via the internal port 148.In this embodiment, the feed gases may be SO₂, H₂O and O₂ which areintroduced via the gas feed inlet 108. The optional fluorine containinggas or gases may be provided downstream by introducing through theinjection port 150 into the reaction medium which is being transportedfrom the first chamber 142 to the second chamber 144. It should be notedthat the injection port 150 may also be used to inject water vapor forsalvation as described below with respect to other embodiments of thepresent invention.

Additionally, the chamber walls 104 and the plasma confinement plate 146which also constitute walls of the internal port 148 may be grounded.This grounding of the walls attracts any charged species causing them tocollide with the walls thereby helping to prevent the charged species(ions) from flowing from the first chamber 142 into the second chamber144.

The present invention can also be performed using a microwave powereddownstream plasma process chamber. FIG. 6 schematically illustrates adownstream photoresist stripping chamber (“downstream chamber”) 300 inaccordance with one embodiment of the present invention. The downstreamchamber 300 includes chamber walls 302, a chamber bottom 304, and achamber top 306, which define a chamber internal region 308. Asemiconductor wafer support structure (or “chuck”) 310 is positionedwithin the chamber internal region 308 near the chamber bottom 304. Thechuck 310 may contain a number of lifting pins 312 that are used toraise and lower a semiconductor wafer (or “wafer”) 314 placed on thechuck 310 for processing. The chuck 310 may also include a heater 316configured to operate using electric power. The downstream chamber 300also includes exhaust system (not shown).

The downstream chamber 300 further includes an applicator tube 320positioned above the chamber top 306. The applicator tube 320 isconfigured to be in open communication with the chamber internal region308 via a shower head 322. A processing gas supply line 324 is in fluidcommunication with the applicator tube 320 to supply a processing gas.The purpose of the applicator tube 320 is to couple microwave energy tothe feed gas and to deliver the dissociated reactive gas mixture to theprocessing chamber 300. The shape of the applicator tube 320 is notlimited to that illustrated in FIG. 6, and the applicator tube may havea different shape such as an elongate tube with an opening at the end.In the embodiment of the present invention, the preferred processing gascontains sulfur (S), oxygen (O), and hydrogen (H). For example, theprocess gas contains SO₂, H₂O and O₂ as feed gases. The process gas mayfurther contain fluorine containing gas, for example, NF₆, NF₃, orfluorocarbon, for example, CF₄. More generally, fluorocarbon may beexpressed as C_(x)F_(y) (x≧1, y≧1) and/or C_(x)F_(y)H_(z) (x≧1, y≧1,z≧1). However, the processing gas supply line 324 can be configured tosupply virtually any type of processing gas.

A microwave power supply 326 is also connected to the applicator tube320 to supply microwave power to the processing gas within theapplicator tube 320. The microwave power generates a plasma andtransforms the processing gas into a reaction medium containing radicalsas its constituent elements. Thus, the applicator tube 320 functions asa first chamber for generating the reaction medium via plasma. Inaccordance with one embodiment of the present invention, a plasma withSO₂, H₂O and O₂ feed gases will generate radicals: HSO₄. monosulfateradical with properties of sulfuric acid, HSO₃. bislufite radical, HO.hydroxyl radical; and O. oxygen radical. The radicals include primarilyH radicals and O radicals. The radicals flow through the shower head 322into the chamber internal region 308 toward the wafer 314. The radicalsisotropically (i.e., uniformly in direction) contact the wafer 314 andreact to remove materials present on the surface of the wafer 314. TheHSO₄. and HSO₃. radicals are strong hydrogen donors such that it canhydrogenate the carbon in the photoresist. Additionally the HSO₄.radical is a strong oxidizing compound such that it along with HO. andO. oxidize the weakened carbon.

FIG. 7A schematically illustrates another example of a plasma module(stripper module) 400 having temperature control in accordance with oneembodiment of the present invention. The stripper module 400 includes aplasma source (with a plasma chamber) 402 and a process chamber 408. Theplasma source 402 energizes a process gas 404 into plasma 406, forexample, using a microwave or RF-powered source. The process chamber 408includes a chamber top 410 having a central opening, a gas distributioncomponent 412 secured to the chamber top 410 at the central opening, aninternal chamber body 414, a temperature controlled chuck 420 forsupporting a substrate (wafer) 422 thereon, and an external chamber body416 that slidably mounts the internal chamber body 414 thereon andsurrounds the side of the internal chamber body 414. The stripper module400 also includes an exhaust unit 450 coupled thereto. The exhaust unit450 may include an isolation valve 452 and a throttle valve 454 coupledto a vacuum pump 456. The plasma module 400 may also include one or moreheaters 424 and fluid cooling channels 426.

The inlet of the central opening of the chamber top 410 is aligned withthe outlet of the plasma source 402. The gas distribution component 412has a plurality of gas passages 442 formed therein, which are configuredsuch that the gas exiting from the gas passages is dispersed anduniformly fanned out. The outlet of the central opening is in fluidcommunication with the inlets of the gas passages 442. The internalchamber body 414 is positioned beneath the gas distribution component412 and includes an upper chamber dome that has a streamlined innersurface to reduce flow recirculation and turbulence and including a sideportion that surrounds the substrate 422 and chuck (support) 420 in thecircumferential direction of the chuck 420. However, the presentinvention is not limited to those specific configurations of thechamber.

A plasma is generated in the plasma source (chamber) 402 from theprocess gas containing sulfur (S), oxygen (O), and hydrogen (H), forexample, a process gas containing feed gases of SO₂, H₂O and O₂, and anoptional fluorine containing gas. A radical-rich ion-poor reactionmedium flows downstream from the plasma 406 into the internal chamberbody 414 of the process chamber 408 through the central opening and thegas distribution component 412.

In addition, an additional gas injection port 440 a may be provided, forexample, through a gap 432 between the internal chamber body 414 and thechamber top 410, as shown in FIG. 7B. In this case, the optionalfluorine containing gas may be introduced through the gas injection port440 a into the internal chamber body downstream the gas passages fromthe gas distribution component 412. Alternatively, as shown in FIG. 7Cthe additional gas injection port 440 b may be provided downstream theplasma source 402 at the conical section above the gas distributioncomponent 412, so as to inject the additional gas containing fluorine.

In accordance with one embodiment of the present invention, the methodfor removing the photoresist further includes solvating the reactionmedium before reaching the plasma. To facilitate understanding, FIG. 8is a flow chart of the salvation process of the reaction medium beingtransported from the plasma to the wafer (during the step 206 in FIG.2). As shown in FIG. 8, water vapor is introduced in an injection orsalvation zone that is provided in a passage of the reaction mediumflowing down from the plasma or the plasma source toward the wafer (step220). The water is forced through a nozzle or orifice to ensure mildcondensation as clusters around ions or radicals.

The water vapor solvates the reaction medium to form solvated clustersof species (step 222) before the reaction medium reaches the wafer. Themeans to achieve clustering (or salvation) is by injecting the watervapor through a fine orifice such that small amount of condensationoccurs. This would be condensation around the specific molecule or ion.This downstream injection is operated such that the water vapor enteringinto the flowing reaction medium (discharge stream) is allowed tocondense around species of the reaction medium generated in the plasmato form solvated clusters. These solvated clusters include either anactive radical or ion surrounded by a number of water molecules. Thenumber of the water molecules may range from 3 to roughly 20, moregenerally, 2 to 100.

In this specification and claims, when the radicals are solvated, itmeans that clusters of water molecules are formed around activeradicals, and the zone where the water vapor is injected and theradicals are solvated is referred to as a solvation zone. As theradicals are transported to the wafer, the reaction on the surface ofthe photoresist is microscopically aqueous. The formation of theclusters depends on the pressure differential between the gas feed lineand the injection zone, as well as on the orifice size. The radicals aresolvated as:

HSO₄.+nH₂O→{(SO₄.)(H₂O)_(n)}

The number n may be in the range of 2 to 100 when the mild condensationoccurs.

If the number of solvating water molecules is large enough, a singleneutrally charged cluster can deliver both positive and negative ions:

H₂SO₄+nH₂O→{(SO₄ ²⁻)(H₃O)⁺ ₂(H₂O)_(n−2)}

In accordance with one embodiment of the present invention, thesalvation zone is provided in the first chamber downstream of the plasmasuch that the reaction medium is solvated before the reaction mediumenters into the second chamber. For example, as shown in FIG. 9, anadditional water vapor inlet 130 may be provided to the plasmaprocessing module 100 (FIG. 3) so as to inject water vapor. The reactionmedium is solvated in a salvation zone 132. The salvation zone in thisembodiment is in close proximity to the plasma generation zone. Thisensures maximum interaction of the water with the plasma. It should benoted that if the salvation zone is too close to the plasma, it mayresult in dissociation of water molecules and breaking of the clusters,and thus the proximity should be well controlled.

In accordance with another embodiment of the present invention, thesalvation zone is provided in a passage of the reaction medium betweenthe first chamber and the second chamber. For example, as shown in FIG.10, the injection port 150 in the plasma processing module 180 (FIG. 5)can be used as an additional water vapor inlet 130 to inject watervapor. The reaction medium is solvated in the internal port 148. Thesalvation process may continue while the reaction medium is transportedinto the second chamber 144. The salvation zone is removed from theplasma generation zone to prevent the water vapor from being dissociatedand prevent the clusters from breaking up.

In accordance with yet another embodiment of the present invention, thesalvation zone is provided in the second chamber such that the reactionmedium is solvated before the reaction medium reaches the wafer. Forexample, as shown in FIG. 11A, an additional water vapor inlet 130 maybe provided to the plasma processing module 140 (FIG. 4A) so as toinject water vapor. Alternatively, as shown in FIG. 11B, the additionalinjection port 150 in the plasma processing module 160 (FIG. 4B), can beused as an additional water vapor inlet 130 to inject water vapor. Inaddition, as shown in FIG. 12, an additional water inlet 130 may beprovided to a downstream chamber 300 (FIG. 6) so as to provide asalvation zone 132. The reaction medium is solvated in the salvationzone 132 in each of these examples. These configurations place thesalvation zone further down stream from the plasma source ensuringcomplete clustering without interference from the plasma, since theplasma may breakup the clusters and even dissociate the water if thesalvation zone is too close to the plasma.

FIG. 13 schematically illustrates an example in which the second chamber144 of the plasma module 500 includes more than one baffles (gasdistribution components). The additional water vapor inlet may beprovided either above the upper baffle 124 a (water vapor inlet 130 a),between two baffles 124 a and 124 b (water vapor inlet 130 b), or belowthe lower baffle 124 b (water vapor inlet 130 c).

In addition, in the plasma processing module 400 a (FIG. 7B) or 400 b(FIG. 7C), the additional gas injection port 440 a or 440 b can be usedas a water vapor inlet 430 a or 430 b so as to introduce water vapor tosolvate the reaction medium, as shown in FIG. 14A and 14B. As discussedabove, the water vapor inlet 430 a may be provided through a gap 432between the internal chamber body 414 and the chamber top 410 so as tohave an opening in the internal chamber body 414. In this case, thereaction medium is solvated in the internal chamber body (the secondchamber) 414 in the salvation zone 132. Alternatively, the additionalwater vapor inlet 430 b may be provided downstream the plasma 406 at theconical section above the gas distribution component 412. In this case,the reaction medium is solvated in the salvation zone 132 (the conicalsection) before entering into the internal chamber body 414 through thegas distribution component 412. The salvation zone in FIG. 14A ensuresthat predominantly radicals will be solvated since the gas distributioncomponent 412 will reduce (or possibly eliminate) ion flux. In contrastthe configuration of FIG. 14B ensures that a larger fraction of ions aresolvated at the expense of dissociating the water vapor or breaking theclusters. The gas distribution component 412 is configured to maximizeion pass through. In other words, the distribution holes in 412 arelarge enough to ensure ion passage.

Furthermore, in accordance with one embodiment of the present invention,a distance between the plasma 406 and the solvation zone 132 can beadjusted. For example, in the plasma process module 400 a (FIG. 14A) or400 b (FIG. 14B), the conical section and plasma source 402 may beraised or lowered with respect to the water vapor inlet 430 a or 430 b.

In accordance with another embodiment of the present invention, ionsfrom the plasma may be permitted to be present in the reaction medium toreach the wafer. The objective is to force negative ions from the plasmainto the solvation zone and form negative ion clusters. Since negativeions do not escape a plasma and congregate in the middle of the plasma,the plasma needs to be shut off in order to get the negative ions out.This is accomplished by pulsing the plasma on and off. That is, themicrowave or RF power to the applicator 402 is pulsed, and if there is abias power then that power would also be pulsed. Typical off times maybe 5 to 50 microseconds, and typical on times may be 5 to 200microseconds. Negative ion production is best under lower pressures. Thenegative ions are solvated and transported to the wafer. Negative ionsare very reactive oxidizing agents, in that they have an additionalelectron over the corresponding radical.

SO₄ ²⁻+nH₂O→{(SO₄)(H2O)_(n)}²⁻

{(SO₄)(H2O)_(n)}²⁻+C—C→{CO₂(H2O)₁}+{SO₂(H2O)_(m)}

This may be achieved by making the exit holes to the second chamberlarge enough. For example, in FIGS. 14A-14B, the gas distributioncomponent 412 may have a plurality of gas passages 442 having largerholes such that ions pass from the plasma discharge zone 406 through thelarger holes into the internal chamber body (the second chamber) 414.The same applies, for example, to the process module 100 (FIG. 9), theopenings of the baffle 124 may be enlarged. In the process module 140(FIG. 11A), the process module 160 (FIG. 11B), and the process module180 (FIG. 10), the opening of the inner port 148 interconnecting thefirst chamber 142 and the second chamber 144 (or reaction chamber) canbe made larger enough such that more ions will pass through. Similarly,in downstream chamber 300 (FIG. 12), the holes of the showerhead 322 canbe made larger.

In addition, if the process module includes an RF power source for thelower electrode (chuck), for example, the process modules 160 or 180, abias voltage can be provided so as to attract the charged species (ions)toward the wafer. The bias voltage may have a frequency of 13.56 MHz andabove, for example, 27 MHz. In these cases, the holes of the baffles canalso be enlarged. Furthermore, the top RF power source to generateplasma may be pulsed to release negative ions. In general, a continuousplasma has a sheath which prevents relatively bulky negative ions fromgetting past the sheath boundary. As the plasma is turned off, thesheath collapses and the negative ions are released. The quartzbaffle(s) may be biased such that the negative ions will pass throughthe quartz baffle, for example, in the process module 100 (FIG. 10).

In addition to negative ions, positive ions will also be transported.Ions such as H⁺ and H₃O⁺ are strong reducing agents. The combination ofoxidation with negative ions and reduction with positive ions willeffectively breakdown the photoresist while checking excessive oxidationor reduction of the active area silicon.

In all of those embodiments of this invention, the addition offluorocarbons is employed to assist in the breakthrough of implantgenerated crust. The fluoride radical and negative ions are very strongoxidizers for breaking through cross-linked carbon bonds.

In accordance with another embodiment of the present invention, thetiming/sequence of introducing the process gas(es) and the water vapormay be changed in order to control effects on the photoresist stripprocess, such as the strip rate, strip residue, amount of material loss,or other on-wafer results in general. When a wafer is placed in thesecond chamber separate from the first chamber where the plasma isgenerated, the timing of introducing the process gases into the firstchamber also controls the timing of the reaction medium to flow into thesecond chamber with respect to the water vapor injection.

According to a first example, the process gas(es) and the water vapormay be introduced/injected into the respective locations in thechamber(s) at the same time. In a second example, the water vapor isfirst injected, followed by the process gases after a certain timedelay. This may have different surface kinetics, and may enhanceabsorption. Alternatively, the process gases are introduced first,followed by injection of water vapor after a certain time delay. Thissequence also has different surface kinetics. In accordance with a forthexample, water vapor is first injected, then only the process gasses areintroduced (i.e., the water vapor injection is being stopped during theintroduction of the process gasses), followed by water vapor injectionwithout introducing the process gases, followed by the process gasesintroduction without water vapor injection, and so forth. The forthexample is an alternating process in which the water vapor and theprocess gases are introduced in an alternating and sequential manner.This may enhance surface absorption and reaction. The sequence (“waterfirst” or “process gas first”) and the time duration of eachinjection/introduction step may also be controlled to optimize thesurface results.

In accordance with another embodiment of the present invention, adiluent gas may be added to the process gas chemistry in any of theembodiments described above.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and various substituteequivalents, which fall within the scope of this invention. It shouldalso be noted that there are many alternative ways of implementing themethods and apparatuses of the present invention. It is thereforeintended that the following appended claims be interpreted as includingall such alterations, permutations, and various substitute equivalentsas fall within the true spirit and scope of the present invention.

1. A method for removing photoresist from a wafer, the methodcomprising: providing a process gas containing sulfur (S), oxygen (O),and hydrogen (H); generating a plasma from the process gas in a firstchamber; flowing a radical-rich ion-poor reaction medium from the firstchamber to a second chamber where a wafer is placed, the wafer having apatterned photoresist layer thereon; removing the patterned photoresistlayer using the reaction medium; and stopping the reaction mediumflowing into the second chamber.
 2. The method according to claim 1,wherein the process gas contains SO₂, H₂O and O₂.
 3. The methodaccording to claim 2, wherein the process gas further contains fluorinecontaining gas.
 4. The method according to claim 3, wherein the fluorinecontaining gas contains fluorocarbon.
 5. The method according to claim1, further comprising: injecting a fluorine containing gas in asolvation zone provided in a passage of the reaction medium flowing downfrom the plasma.
 6. The method of claim 1, wherein no bias voltage isapplied.
 7. The method of claim 1, further comprising: applying a RFpower to generate bias voltage having a frequency of 13.56 MHz andabove.
 8. The method of claim 1, further comprising: controllingtemperature of the wafer.
 9. The method of claim 1, further comprising:pulsing plasma discharge so as to release negative ions into thereaction medium.
 10. The method according to claim 1, furthercomprising: introducing water vapor in a salvation zone provided in apassage of the reaction medium flowing down from the plasma such thatthe water vapor solvates the reaction medium to form solvated clustersof species before the reaction medium reaches the wafer.
 11. The methodaccording to claim 10, wherein the salvation zone is provided in thefirst chamber downstream of the plasma, the reaction medium beingsolvated before the reaction medium enters into the second chamber. 12.The method according to claim 10, wherein the salvation zone is providedin the second chamber.
 13. The method according to claim 12, wherein thereaction medium is transported to the wafer through at least one gasdistribution component having a plurality of holes which allow thereaction medium to flow therethrough.
 14. The method according to claim13, wherein the water vapor is injected above the gas distributioncomponent.
 15. The method according to claim 13, wherein the water vaporis injected below the gas distribution component.
 16. The methodaccording to claim 13, wherein the water vapor is injected between twogas distribution components.
 17. The method according to claim 10,further comprising: adjusting a distance between the plasma and thesalvation zone.
 18. The method of claim 10, further comprising: pulsingplasma discharge so as to release negative ions into the reactionmedium.
 19. An apparatus for removing photoresist from a wafer, theapparatus comprising: a first chamber for generating a plasma from aprocess gas, the first chamber having a gas inlet; a gas source in fluidconnection with the gas inlet, for providing the process gas containingsulfur (S), oxygen (O), and hydrogen (H) into the first chamber; asecond chamber for placing the wafer having a patterned photoresistlayer thereon; a reaction medium distributing section for flowing aradical-rich ion-poor reaction medium from the plasma in the firstchamber to the second chamber; and a water vapor inlet provided to thesecond chamber or the reaction medium distribution section, the watervapor inlet introducing water vapor in a salvation zone provided in apassage of the reaction medium flowing from the plasma to the wafer suchthat the water vapor solvates the reaction medium to form solvatedclusters of species before the reaction medium reaches the wafer. 20.The apparatus of claim 19, wherein the water vapor inlet includes: anozzle configured to inject the water vapor so as to condensate asclusters around the species.